In wireless communication networks, one or more subscriber stations (SSs) receive traffic from a base station (BS) in a downlink (DL) channel and transmit traffic to the BS in an uplink (UL) channel. The DL channel is a broadcast channel because transmissions by the BS can be received by all of the SSs that are in a coverage region of the BS. However, different parts of the DL transmission may be destined for different SSs. Therefore, the BS may inform the SSs about their allocations in a DL frame before it transmits the traffic destined for specific SSs in the DL channel. Hence, different SSs learn about the locations of their traffic, if any, using the allocation information in the DL frame and process only the portions of the DL channel that contain their traffic.
The Institute of Electrical and Electronics Engineers (IEEE) standards, such as 802.16d and 802.16e, specify different methodologies for a BS to inform the SSs about the allocations in the DL frame, which are valid for both time division duplex (TDD) and frequency division duplex (FDD) systems and derivatives thereof, such as half-duplex FDD (HFDD) systems. The BS specifies the allocations in one or more information elements (IEs) of a downlink map (DLMAP), which contain information about a particular portion of the DL channel, known as a DL burst. A SS decodes the DL-MAP to learn about the DL bursts that contain, or may contain, its traffic. A DL burst that contains traffic for a SS corresponds to the scenario in which the DL-MAP-IE contains an identification of connections for Media Access Control Protocol Data Units (MAC PDUs) that are present in a particular DL burst. A DL burst that may contain traffic for a SS corresponds to the DL-MAP-IE not containing the identification of the connections for the MAC PDUs present in a particular DL burst.
In the 802.16d/e standards, the connections are identified using Connection Identifiers (CIDs). A SS may have multiple CIDs for its different connections. Where the DL-MAP-IE does not contain the CIDs for the MAC PDUs present in DL burst, a SS may choose to process that burst to search for its MAC PDUs. The SS searches for its MAC PDUs using the header of the MAC PDUs that contain the information about the desired receiver(s) of the MAC PDUs. In the 802.16d/e standards, the intended recipient of a MAC PDU is specified by the CID field of the MAC PDU header.
In the 802.16d/e standards, the BS informs the SSs about the allocations for the UL channel using an UL MAP containing UL-MAP-IEs that specify the allocations for different UL bursts. The UL-MAP-IEs inform different SSs about their allocations in the UL channel, which are used by the SSs to transmit their MAC PDUs to the BS.
Each MAC PDU can belong to a unicast, multicast or broadcast connection. The CID field identifies the intended receiver or the group of intended receivers for unicast and multicast connections respectively. A broadcast PDU is intended for all the receivers indicated by the broadcast CID present in the header of the MAC PDU.
The CIDs of the MAC-PDUs contained in a particular DL burst may or may not be specified in a DL-MAP-IE. This is indicated by the INC_CID field in the DL-MAP-IE. When INC_CID=0, CIDs of the MAC PDUs in a DL burst are not specified in the corresponding DL-MAP-IE. When INC_CID=1, the CIDs of the MAC PDUs are specified in the corresponding DL-MAP-IE.
When INC_CID=0, it is not clear to a SS if its MAC PDUs are present in the corresponding DL burst. Therefore, the SS may process the contents of the corresponding DL burst to learn the presence or absence of its PDUs. Thus, when INC_CID=0, the SS has to process the entire DL burst even if there are no PDUs destined for it in the burst. This results in significant power consumption by the SSs, that may be wasted if there are no PDUs for it in the burst.
When INC_CID=1, a SS learns of the presence or absence of its MAC PDUs in the corresponding DL burst from the CIDs specified in the DL-MAP-IE. If a SS finds one or more of its CIDs present in a DL-MAP-IE, it learns that its MAC PDUs are present in the corresponding DL burst. Otherwise, the SS learns of the absence of its MAC PDUs in the DL burst. Therefore, when INC_CID=1 the SS processes the DL burst only if the corresponding DL-MAP-IE contains its CIDs.
Similarly, in the UL, CIDs are used in the UL-MAP-IEs to indicate the allocations of the UL bursts. Moreover, CIDs are used in the header of the MAC PDUs to indicate the connection to which the MAC PDU belongs.
Skilled addressees will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the relative dimensions of some of the elements in the figures may be distorted to help improve understanding of embodiments of the present invention.